Thread about implementing STM on Lispworks:

http://article.gmane.org/gmane.lisp.lispworks.general/9700/m...

If they only did this in OCaml, once it's established...

Isn't there an attempt to do STM in OCaml already underway?

Anyway, you will have to refrain from (almost) any side-effects while inside an STM transaction. That comes naturally to Haskell --- but in OCaml they tend to be used them more often as far as I know. This requires some discipline.